Turbochargers are provided on an engine to deliver air to an engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
Generally, turbochargers use exhaust flow from an engine exhaust manifold, which exhaust flow enters a turbine housing at a turbine inlet, to thereby drive a turbine wheel, which is located in the turbine housing. The turbine wheel provides rotational power to drive a compressor wheel of the turbocharger. This compressed air is then provided to the engine intake as referenced above.
Referring in more detail to a representative turbocharger 10 shown in the cross-sectional view of FIG. 1, the turbocharger 10 includes a turbine housing or casing 12 having a volute 14 extending circumferentially therein, a compressor housing 16 and a compressor volute 17, and a turbine wheel 18 and a compressor wheel 19 that are rotatably connected together by a shaft 21. The shaft 21 is supported by a bearing system 22 which is supported within a central bearing housing 23 disposed between the turbine housing 12 and the compressor housing 16. The bearing housing 23 defines a bearing chamber 24 which extends axially between the compressor housing 16 and turbine housing 12 to allow the shaft 21 to extend axially therebetween so that rotation of the turbine wheel 18 drives rotation of the compressor wheel 19 during operation of the turbocharger 10.
In this illustrated turbocharger 10, the bearing system 22 typically includes a journal bearing 25 positioned within the bearing chamber 24 to provide radial support to the rotating shaft 21. For reference purposes, the Z direction extends axially along the central axis of shaft 21, while the X and Y directions extend radially outwardly therefrom. An end view of the shaft 21 and turbocharger 10 is viewed along the Z direction while the side view is taken in the X direction. These directions are for reference and viewing purposes and are not intended to be limiting.
FIGS. 2 and 3 illustrate one example of a known bearing configuration, which is currently in commercial use. In this configuration, axially-spaced, floating ring bearings 30 are provided which are slidably received within the bearing chamber 24 and surround the shaft 21. More particularly, each floating ring bearing 30 is located radially between a radially inward-facing chamber surface 31 of the bearing housing 23 and a radially outward-facing shaft surface 32 of the shaft 21. The floating ring bearings 30 are axially separated from each other along the Z direction by a cylindrical bearing spacer 33, wherein each floating ring bearing 30 is able to float or move radially to a small extent during shaft rotation. The floating ring bearings 30 function to radially support the shaft 21 and prevent radial contact between the shaft 21 and bearing housing 23 in response to radial loads on the shaft 21.
To support axial shaft loads along the Z direction, the bearing system 22 also includes an annular thrust bearing 35 which has opposite end faces 36 which face in opposite axial directions. On one side, one end face 36 faces axially toward an opposing face of the bearing housing 23 and a thrust washer 37 which is supported on the shaft 21. The opposite end face 36 faces towards an annular insert 38 which is supported on the bearing housing 23. The thrust bearing 35 is fixed axially between the opposed faces of the insert 38, thrust washer 37 and bearing housing 23 and is thereby able to accommodate axial shaft loads.
To dampen the radial and axial movements caused by shaft rotation, a fluid such as oil is supplied to the bearing chamber 24 which oil is able to flow around the floating ring bearings 30 and the thrust bearing 35. The oil is supplied to the bearing chamber 24 through an inlet passage 39 which feeds two oil feed ports 40 that supply oil to the floating ring bearings 30 and feeds an additional oil feed port 41 that supplies oil to the thrust bearing 35.
As to the floating ring bearings 30, the oil thereby surrounds the outside and inside circumferential surfaces of the bearings 30. During shaft rotation, an inner fluid film is formed on the inside bearing surfaces which defines a journal bearing supporting the shaft 21 radially. The outside bearing surfaces also have an outer fluid film formed thereabout which provides radial support to the floating ring bearings 30. The outer and inner films form between the outer and inner bearing surfaces and the respective chamber surface 31 and shaft surface 32. As to the thrust bearing 35, fluid films also are formed between the bearing surfaces 36 and the opposed surfaces of the insert 38 and thrust washer 37 to support axial shaft loads.
Despite the foregoing, disadvantages can still exist with this known bearing configuration.